Various solutions have already been proposed in the prior art, for covering a surface of a substrate, in relative motion or otherwise, with a fluid material (liquid or powder for example).
All the proposed solutions have in common on the one hand the prior formation, by overpressure or under vacuum, of a turbulent mixed flow obtained by mixing, with entrainment if necessary, of a controlled fluid stream comprising the fluid covering material, and of a gas stream, and on the other hand various arrangements making it possible to recover the unused or unconsumed turbulent mixed flow so as to avoid its diffusion into the ambient air.
In accordance with document WO-92/12803, and in particular according to the embodiment described with reference to FIGS. 22 to 24, and from line 11 of page 27 to line 33 of page 29, there is described an installation for covering the surface of a substrate 643 with a fluid material.
This installation comprises a means of treatment comprising a confining wall 657, with an edge defining the area to be treated. A means 666 makes it possible to establish a controlled vacuum inside the area to be treated, by admitting several incoming gas streams 684 and 680, through the aforesaid void. A means of controlled introduction, or head 642, into the area to be treated of the fluid material 644, associates a controlled flow void with a pressurized air inlet 645/446, so that a turbulent mixed flow 682/683, circulating in contact with the substrate 643, is produced directly at the head outlet; cf. page 27, lines 14 to 21.
The incoming air streams 684 and 680 are all formed only so as to contain the turbulent mixed flow in the area to be treated; cf. for example page 29, lines 1 to 4, and lines 25 to 30.
In accordance with document WO-79/00469, a turbulent mixed flow is obtained by previously mixing a controlled fluid stream (3) comprising the fluid covering material, and a gas stream, these two streams being under overpressure so as to eject the mixed flow through a distribution vessel (5). Two successive confining walls of cylindrical shape form two concentric peripheral volumes 6 and 7, under vacuum, so as to discharge the turbulent mixed flow after its contact with the surface to be covered.
In accordance with document GB-1 134 069, a turbulent mixed flow is obtained, under vacuum, by mixing a fluid stream (powder) and a gas stream. The turbulent mixed flow resulting from this circulates as a co-current, still under vacuum, in contact with the surface of an elongate substrate moving translationally.
In accordance with document WO-96/09122, a nozzle for spraying a powder is described, making it possible to eject under pressure a turbulent mixed flow obtained previously by mixing a fluid stream (powder) and a gas stream. The unused mixed flow is reaspirated around the nozzle by appropriate means.
At the conclusion of this examination, all the prior solutions have the common characteristic of pushing as it were the fluid material onto the surface of the substrate to be covered. This characteristic may prove to be inefficient for covering substrates with an irregular surface, for example a porous surface.